The present invention relates generally to methods and apparatus for forming servo patterns, and more particularly to such methods and apparatus for forming servo patterns on glass discs for use on a magneto-optical disc drive.
Traditional disc drives are storage information devices that use rotating thin film media to store data. A hard disc drive includes one or more rotatable discs each having closely spaced concentric data tracks. Each track is further subdivided into sectors wherein data is stored. As a disc rotates, a transducer (or head) is positioned by an actuator to read data from or write data to the various sectors within the tracks on the disc.
Prior to a disc drive""s use in a computer, formatting information is written to disc surfaces in the drive. This formatting information can include, for example, the location of each data storage sector, sector number identification information, the start of a group of sectors, and servo pattern information. Disc formatting information enables essential drive operations and/or provides for improved disc drive operation or features. For example, as described below, servo pattern information which is essential to maintain a drive""s head alignment with the tracks on the disc is stored on the disc.
To accurately read or write data to a disc, the drive""s head or transducer must remain closely aligned with the particular track being accessed. If the head deviates from the track, data may be read or written improperly. This can result in irretrievable data and damage to existing stored data.
To maintain alignment between the head and track, a closed loop alignment system is used. A conventional head alignment systems, markers on one or more disc surfaces are used to guide the heads. These markers, known as servo patterns, provide dynamic head position feedback to a control mechanism. In response to detected servo pattern signals, the control mechanism can adjust head alignment while reading or writing data to the disc.
Servo patterns on a traditional magneto-optical disc with which this invention is especially concerned consists of a pre-embossed pattern array as is well understood in this technology and is described for example in xe2x80x9cThe Physical Principles of Magneto-Optical Recordingxe2x80x9d by Masud Mansuripur, Cambridge University Press 1995. These pits are made on a plastic substrate by an injection molding process with the aid of a master plate. Magneto-optical film is subsequently deposited over the servo pattern. While injection molding provides a low-cost manufacturing process for plastic substrates, it is not suitable for more rigid substrates, such as glass or ceramic substrates. Hence, creating servo patterns on a rigid substrate remains a challenge.
Geometry of the head in a conventional magneto-optical drive which employs remote optical pickup to read/write information does not impose a significant problem. But with a lens incorporated on a Winchester-type flying head, geometry of the system can affect the flyability of the head over the servo pattern.
Servo patterns on a magneto-optical disc could also be written magnetically with a servo writing process similar to that used to create servo patterns in a hard magnetic disc. This process involves bit-by-bit sequential writing, which takes a long time to complete. A disc may have many thousands of tracks; consequently, formatting the disc with servo patterns and/or other formatting information can be a time consuming process. Therefore, present methods and apparatus for writing servo patterns on a rigid substrate remains a problem and a need exists for a solution to this problem.
The present invention provides a solution to this and other problems, and offers other advantages over the prior art.
The present invention relates to a rigid disc substrate for use in a magneto-optical drive, and two methods and apparatus to solve the above-mentioned problems.
In accordance with one embodiment of the invention, a method is provided for writing a servo pattern on a magneto-optical rigid media, after the media optical film is deposited. The method involves an image transfer process, wherein a light source provides an energy pulse to heat up the magneto-optical film above its compensation temperature. Light is directed onto the film through a photo mask which has a prewritten servo pattern on it. The image on the mask is transferred to the magneto-optic disc when an external field is applied by a magnetic field generating coil which defines the area illuminated by the source where the pattern is to be written.
In an alternative approach, the mask is in contact with the media while the light exposure and magnetic field are applied.
In a further alternative, the image transfer is achieved with a scanning method whereby the light source is scanned through the mask with the aid of a scanning device while the external magnetic field is applied. This scanning method applies equally well with projection image transfer or contact image transfer. These and various other features as well as advantages which characterize the present invention will be apparent upon reading the following detailed description and review of the associated drawings.